In-situ TEM-Untersuchungen des durch thermische Spannungen und Elektromigration induzierten Materietransports in Al-Leiterbahnen

Heinen, D.

Book/Report

FZJ-2019-02301

In-situ TEM-Untersuchungen des durch thermische Spannungen und Elektromigration induzierten Materietransports in Al-Leiterbahnen

Heinen, D. (Corresponding author)FZJ*

1997
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Berichte des Forschungszentrums Jülich 3435, VIII, 109 p. (1997)

Please use a persistent id in citations: http://hdl.handle.net/2128/22004

Report No.: Juel-3435

Abstract: Diluted Aluminum alloys are commonly used as interconnect material in integrated electronic devices. Thermally-induced mechanical stresses in these devices which are caused by thermal mismatch between the underlaying Si-substrate and the surrounding passivation are of special interest because degradation effects such as stress induced voiding or electromigration(EM)-damage are closely related to the stresses in the lines. Electromigration-driven mass transport in "near-bamboo" Al-lines, which consist mostly of "blocking grains", is an important topic of research on ULSI-metallizations. Because the most easy diffusion path, i.e. grain boundaries parallel to the line, is suppressed in bamboo-like Al-grain structures other paths have to be considered. One path is EM-driven $\underline{intra}$granular diffusion in Al-lines. In this experiment, inert gas-filled voids with a mean diameter of about 10nm, which were created after gas implantation and annealing of the Al-lines, serve as indicators of mass (or vacancy) transport. The EM-tests which were done by in-situ observations in a transmission electron microscope (TEM) reveal no intragranular void motion over a period of more than 100h at current densities of 1-1.75MA/cm$^{2}$ and temperatures of 150-225°C. This leads to an estimation of the maximum void diffusion velocity which was compared with calculated values of surface and volume diffusion controlled void motion, respectively. This leads to the result that surface diffusionhas to be suppressed because it should have been observable in the TEM. In contrast to that volume diffusion could have been possible but the velocity of this process was below the resolution of the TEM. The other examined path of diffusion was the behavior of dislocations in Al-lines under an applied EM-force. Motion and buckling of dislocations which was dependent on the current direction was observed and explained as a reaction of the stress gradient due to EM-induced mass transport. A further point of interest was the observation of relaxation of thermally induced stresses within the lines by plastic deformation of the Al due to dislocation movement. The behaviour of dislocations during thermal cycling has been examined. The observed formation of dislocation lines in or near the interface behind a onward moving curved dislocation confirms a theoretical model which describes stress relaxation caused by dislocation glide. The third topic of this thesis was the collection of detailed statistical data of stress- and electromigration-induced void formation and growth in $\underline{passivated}$ Al-lines by in-situ TEM experiments. Experimental parameters such as grain size, relaxation time and temperature and electromigration current density were varied. Some important results are: Void nucleation takes place exclusively at the passivation side walls in a very narrow temperature range about 50°C below the annealing temperature T$_{A}$ (450°C $\le$ T$_{A} \le$ 550°C) on cooling. The growth rate of the relative total void volume in the lines is very dependent on time and temperature during isothermal relaxation consistent withprevious data evaluated from macroscopie stress and strain measurements. Although nearly all pre-existing voids change their shape and/or position during an electromigration test the number of voids and their total volume is maintained in excellent agreement with recent X -ray measurements $\underline{during}$ electromigration testing showing no changes in average strain or stress in the lines.

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